1. Field of the Invention
The present invention is related to interactive video display presentation systems and, more particularly, to a method and apparatus for calibrating such a system.
2. Description of the Related Art
In meetings and in classrooms, charts, text, and various graphical images are commonly presented to the audience by means of optical projection onto a projection screen or a wall. An LCD (liquid crystal display) projector is commonly used, where the charts, text, and graphical images are generated by a personal computer (PC), such as a laptop computer. These LCD/PC projection display systems are becoming more popular than the traditional overhead projector and transparencies which they replace. In such display systems, the PC provides video outputs such as standard VGA, Super VGA, or XGA.
The user controls the image being projected onto the projection screen by means of the PC keyboard, or by clicking a mouse in the appropriate area of the computer monitor display screen. Some systems provide limited, remote mouse control by using a line-of-sight infrared signal that is directed at the LCD projector and which controls some predefined functions, such as advancing the presentation to the next frame or drawing a straight line. One such apparatus, comprising radiation sensing means at the projection screen, enables an operator to interact with a computer-controlled image projection system, as disclosed in U.S. Pat. No. 5,235,363 issued to Vogeley et al. However, even with such features, most control operations need to be performed at the PC itself If the speaker is standing at a lectern or moving before the audience, he cannot readily return to the PC to provide control. It becomes necessary to have an assistant seated at the computer to provide the control for certain aspects of the presentation.
In another variation of the display presentation, a laser pointer is used to project a control beam onto the projected image. An imaging device detects the control beam and relays this information to the PC. The user controls the PC by moving and switching the control beam on and off. To provide an accurate reference of the control beam to the displayed image on the PC screen, it is necessary to calibrate, or align, the projected image to the displayed image.